Event handlers

Most event handler properties, of the form onXYZ, are defined on the GlobalEventHandlers or TouchEventHandlers interfaces and implemented by HTMLElement. In addition, the following handlers are specific to HTMLElement.

Added the following properties: translate, itemScope, itemType, itemId, itemRef, itemProp, properties, and itemValue.
Added the following method: forceSpellcheck().
Moved the onXYZ attributes to the GlobalEventHandlers interface and added an inheritance from it.